Chemical impedance detectors for fluid analyzers

ABSTRACT

A chemical impedance detector having several electrodes situated on or across a dielectric layer of a substrate. The electrodes may be across or covered with a thin film polymer. Each electrode may have a set of finger-like electrodes. Each set of finger-like electrodes may be intermeshed, but not in contact, with another set of finger-like electrodes. The thin-film polymer may have a low dielectric constant and a high porous surface area. The chemical impedance detector may be incorporated in a micro fluid analyzer system.

The present application is a continuation of U.S. patent applicationSer. No. 11/383,728, filed May 16, 2006, which claims the benefit ofU.S. Provisional Application No. 60/681,776, filed May 17, 2005, and thebenefit of U.S. Provisional Application No. 60/743,486, filed Mar. 15,2006. U.S. patent application Ser. No. 11/383,728, filed May 16, 2006,is hereby incorporated by reference.

The U.S. Government may have some rights in the present invention.

BACKGROUND

The present invention pertains to detectors and particularly todetectors for fluid analyzers. More particularly, the invention pertainsto chemical impedance detectors.

U.S. patent application Ser. No. 11/383,723, filed May 16, 2006,Attorney Docket No. H0008131 (1100.1371101), entitled “An OpticalMicro-Spectrometer,” by U. Bonne et al., is hereby incorporated byreference. U.S. patent application Ser. No. 11/383,663, filed May 16,2006, Attorney Docket No. H0010160 (1100.1412101), entitled “A ThermalPump,” by U. Bonne et al., is hereby incorporated by reference. U.S.patent application Ser. No. 11/383,650, filed May 16, 2006, AttorneyDocket No. H0010503 (1100.1411101), entitled “Stationary Phase for aMicro Fluid Analyzer,” by N. Iwamoto et al., is hereby incorporated byreference. U.S. patent application Ser. No. 11/383,738, filed May 16,2006, Attorney Docket No. H0012008 (1100.1413101), entitled “AThree-Wafer Channel Structure for a Fluid Analyzer,” by U. Bonne et al.,is hereby incorporated by reference. U.S. Provisional Application No.60/681,776, filed May 17, 2005, is hereby incorporated by reference.U.S. Provisional Application No. 60/743,486, filed Mar. 15, 2006, ishereby incorporated by reference. U.S. patent application Ser. No.10/909,071, filed Jul. 30, 2004, is hereby incorporated by reference.U.S. Pat. No. 6,393,894, issued May 28, 2002, is hereby incorporated byreference. U.S. Pat. No. 6,837,118, issued Jan. 4, 2005, is herebyincorporated by reference. U.S. Pat. No. 7,000,452, issued Feb. 21,2006, is hereby incorporated by reference. These applications andpatents may disclose aspects of structures and processes related tofluid analyzers, including the PHASED (phased heater array structure forenhanced detection) micro gas analyzer (MGA).

SUMMARY

The present invention may be an implementation of chemical impedance(resistive or capacitive) detector of gases or liquids having a low-kporous and permeable, high surface area thin film polymer oninterdigitated electrodes having dimensions compatible withmicro-channels of micro analyzers. The detector may be integrated intothe structure of a micro analyzer.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1 a and 1 b are views of an illustrative structure of a chemicalimpedance detector having a capacitance from co-planar interdigitatedstructures;

FIG. 2 reveals a differential chemical impedance detection system withco-planar interdigitated electrodes, implemented into a micro analyzerhaving flow sensors and thermal conductivity detectors;

FIG. 3 reveals another capacitive impedance detector structureconsisting of an array of holes into a plane-parallel capacitor, withspacings comparable to the thin dielectric, so maximize porosity,sensing signal and analyte access, and minimize response time;

FIG. 4 is a layout of a thermo conductivity detector which may be usedin series with a chemical impedance detector on the same analyzer;

FIG. 5 is a table of examples of porous materials with measured specificsurface area available for general chromatography pre-concentration;

FIG. 6 is an available list of non-porous polymers that aresolvent-castable;

FIG. 7 is an available list of materials to show limit of detectionlevels and immediate danger to life and health levels and acorresponding detection polymer used;

FIG. 8 is a worksheet of a model with porous capacitance information forparameters like those of a micro analyzer;

FIG. 9 is a plot of results of some materials as they relate topartition equilibria;

FIG. 10 lists some numerical results of the toluene and DMMP uptake inseveral polymers noted with partition equilibria;

FIG. 11 shows retention time data relative to a column with DB-5 forDEEP and DMMP;

FIG. 12 shows a table of parameters including partial function valuesfor various analtyes;

FIG. 13 is reveals information for evaluation of separation performanceof general chromatography columns having partial stationary phasecoverage;

FIG. 14 is a graph is a graph of retention time for a number of analytesin a column having one regularly coated and heated wall and thinlycoated, unheated remaining walls;

FIG. 15 shows an illustrative example of chemical impedance detectors ofFIG. 2 situated in a fluid analyzer;

FIG. 16 is a system view of an illustrative phased heater arraystructure for enhanced detection fluid analyzer which may encompass thepresent channel and thermal conductivity detector;

FIG. 17 shows a top view of a phased heater arrangement;

FIG. 18 is a cross section view of the heater arrangement and associatedinteractive elements; and

FIG. 19 shows graphs illustrating a phased heater arrangement operation;

DESCRIPTION

Related art CIDs (chemical impedance detectors), i.e., polymer gaschromatography (GC) detectors, appear to be bulky, slow (about 1second), of low sensitivity and not integrated into the structure of themicro analyzers. Such detectors, whether based on changes inresistivity, dielectric constant or strain of the polymer, shouldachieve a gas-to-solid solution equilibrium, which is either too slow(for high-speed GC applications), due to the slow rate of diffusion intothe polymer lattice, or too insensitive, due to low film thicknessrequired if the response time is to be lowered.

FIGS. 1 a and 1 b show an illustrative example of an interdigitatedcapacitive polymer detector 10, viz., a chemical impedance detector(CID). FIG. 1 a reveals a top view and FIG. 1 b shows a cross-sectionview of the detector 10 at line 30 of FIG. 1 a. A layer 12 of dielectricmay be situated on a substrate 11. For an illustrative example, thesubstrate 11 may be silicon and layer 12 may be SiO₂. Substrate 11 andlayer 12 may be of some other appropriate material. On the SiO₂ layer 12may be finger-like electrodes 13 and 14 intermeshed with each other butnot in contact with each other. On the electrodes 13 and 14 and the SiO₂layer 12 portions between the electrodes may be a layer 15 of a thinfilm polymer. The CID 10 may have a larger or even a smaller structureother than the one shown in the Figures.

The CID 10 may solve related-art shortcomings by using low-k-porous,high surface area (for low stray capacitance and high sensitivity)thin-film (for ms-level speed) 15, on interdigitated pairs of low-heightand low-width electrodes 13 and 14 (to maximize signal/stray capacitanceratio), compatible with micro-channel dimensions (for short purge times)of a fluid analyzer, such as a phased heater array structure forenhanced detection (PHASED) micro gas analyzer (MGA).

FIG. 2 shows a layout of two CIDs 10 on a chip 21. An insert 22 which isan enlarged area of a CID 10 reveals an interdigitization of thefinger-like portions of electrodes 13 and 14. A gas to be detected mayenter an inlet 23, and then pass through a three element flow sensor 24and a thermo conductivity detector 25. From the detector 25 the gas maygo through the CID 10 for detection and a determination of a magnitudeof an amount of a particular analyte. From there, the gas may exit fromCID 10 to the gas outlet 26. Both CIDs 10 may connected and operated ina differential AC-coupled mode where one is exposed to the analyte peaksand the other is not, or to one of a different composition orconcentration.

FIG. 3 reveals another capacitive impedance detector structure 49consisting of an array of holes 47 into a plane-parallel capacitor 48,with spacings comparable to the thin dielectric, so maximize porosity,sensing signal and analyte access, and minimize response time.

FIG. 4 shows a layout of an illustrative example of a thermalconductivity detector (TCD) 25 which may be used in conjunction with theCID 10. A sample gas flow 27 may pass over a detector element 28. Thestructure of detector 25 may include a wall 33, membrane supports 29 andair gaps 31 on both sides, provided that both sides are sealed relativeto the sample analyte being analyzed; otherwise, there would not be airgaps 31 present in the structure of detector 25. Lead-outs 32 may beconnected to the detector element 28. Dimension 34 of the detector maybe about 100 microns.

Polymer film-based sensors, in general, upon exposure to trace gases,may either change film resistivity, dielectric constant, strain and/orweight. Also, metal oxide films may change resistivity and serve asdetectors. The porous, spin-coatable materials may be used for GCpre-concentration and separation. Pre concentration or a preconcentrator may be referred to as concentration or a concentrator,respectively, even though it may be actually like pre concentration or apre concentrator.

Also, polymer films may be used for gas detection in gas chromatographyin the form of SAW detectors (surface acoustic wave, sensitive tochanges in film mass). Useful detector results may be obtained with MPN(dodecanethiol monolayer protected gold nanoparticle) films, whichchange in electrical conductivity when exposed to different gases. Thesefilms may have excellent results when used as GC separator films incapillary columns.

A table in FIG. 5 shows examples of porous materials with measuredspecific surface area used for GC pre-concentration in packed columnsbut typically not necessarily as solvent-castable films. This table mayprovide characteristics of selected adsorbents, such as maximumtemperature (° C.), specific surface area (m²/g), pore size (nm), andthe respective monomer.

A table in FIG. 6 lists non-porous polymers that are solvent-castable.This table provides information relating to detector polymers forsolvent casting and stable to 250° C. in inert atmospheres. Films ofrubbery (Tg<operating temperature) polymers 100-200 nm in thicknessappear to be consistent with fast response times (˜milliseconds). Asample gas velocity of 1 m/s may pass a 1-mm long in only about 1 ms.The table of FIG. 6 lists a chemical name, acronym, character andapplication.

A table in FIG. 7 lists performance in terms of a ppm-level LOD (limitof detection), in relation to the IDLH (immediate danger to life andhealth) or ppm-level of IDLH, for an analyte detector of industrialsolvent vapors, CWA (chemical warfare agent) simulants and ERCs(explosives-related compounds), along with the polymer used fordetection. The table may reveal a LEL (lower explosive limit) and anIDLH concentration for selected VOCs (volatile organic compounds), withthe lowest detected vapor concentrations and a calculated theoreticalLOD in ppm (v/v), signal-to-noise ratio (S:N, measured response involts/peak-to-peak noise in volts), the polymer used to achieve thelowest detected concentrations, and the oscillation amplitude(ΔV_(OSC)).

In order to enable detector performance prediction and comparisonbetween alternate materials, one may define some polymer propertiesrelated to their ability to absorb gases: 1) Directly measurable viagas-weight absorption into polymers are partition function values, K,(which are geometry-independent thermodynamic equilibrium values forfilm materials before and after exposure to analytes); and 2) Alsomeasurable via GC elution or retention times are partition or capacityfactors, k′. A comparison between these two is possible by rememberingthat K=k′·β, where β=volumetric ratio of the gas/film volume of a GCseparation column. The values of k′=(t_(r)−t_(o))/t_(o) depend on theratio β and thus on the column ID and film thickness. For example, underotherwise equal conditions, larger ID columns may cause the analyte toreside a greater fraction of the time in the gas phase, and thus beswept through the column within a time closer to that of the unretainedanalytes, t_(o), thus resulting in smaller k′ values than would be thecase with smaller IDs. A similar argument may be made for filmthickness. One may herein compare K-values derived from weight gainmeasurements with GC-derived k′ values obtained for a porous filmmaterial, in order to estimate likely detector performance.

Another source of K and k′ data is provided by theoretical predictions,as can be made via molecule-surface energy interaction models, which canthen result in predictions of capacitance detector signal and a film'ssensitivity to exposure to given analytes. Such models generatemolecular internal energy changes, ΔE, corresponding to the ad- orabsorption of a gas molecule on the surface (liquid or gas). Therelation between ΔE and K follows known laws of thermodynamics, whichrelates changes in ΔE to changes on enthalpy, ΔH; entropy, ΔS; Gibbs'Free Energy, ΔG; and the equilibrium constant, K: ΔH=ΔE+TΔS; andΔG=RT·ln(K)=ΔH+TΔS.

The present CID 10 two capacitors, for which the capacitance is given byC=N.(Ca+Cd), where Ca=2.ε_(o).D(k₁)/D′(k₁) capacitance in air,Cd=2.ε_(o).ε_(r).D(y₁)/D′(y₁) capacitance in the substrate, ε_(o)=0.0886pF/cm=dielectric constant of vacuum, ε_(r)=relative dielectric constantof the substrate material, D(y), and D′(y) represent the completeelliptic integral of the first kind and its complement, y=W/(W+2s), Wthe metal width and s the spacing, respectively.

The ratio D(y)/D′(y) is simplified to

${\frac{D(y)}{D^{\prime}(y)} = {{\frac{\pi}{\ln \left( {2\frac{1 + y^{\prime}}{1 - y^{\prime}}} \right)}\mspace{14mu} {for}\mspace{14mu} 0} \leq y \leq {1/\sqrt{2}}}},{\frac{D(y)}{D^{\prime}(y)} = {{\frac{\ln \left( {2\frac{1 + y}{1 - y}} \right)}{\pi}\mspace{14mu} {for}\mspace{14mu} {1/\sqrt{2}}} \leq y \leq 1}},$

where y′=√{square root over (1−y²)}.

To achieve a response time near 1 millisecond, the plate height and thefilm thickness (to enable rapid analyte in- and out-diffusion) should bet₂˜h˜0.1 μm, which also requires W to be near that dimension. However,fabrication technology may just allow values of W˜1 μm.

FIG. 8 lays out a model of porous capacitance information for parameterslike those of a micro analyzer, such as a PHASED MGA 110 (FIG. 16). Theabove calculations may be compiled into a table in FIG. 8, where thedata input cells are highlighted with dashed-line boxes and the CIDoutputs (signal and background) and results in dotted-line boxes, for asimple alkane such as hexane. Larger molecular weight and more denseanalytes may lead to larger ΔC signals. Note, however, that these may begenerally maximum ΔC estimates, based on assumption that the analyteconcentration on the polymer 15 would be one monomolecular layer, whileignoring gas-phase analyte concentrations and equilibrium partitions.

One may evaluate non-porous-film type CIDs. An ability to dissolvegaseous analytes into the structure of a polymer may be given by thesolubility mass fraction, μ, which is closely related to the partitionfunction or equilibrium whereμ=m(vap-in-film)/m(film)=Δm(film)/V(film)/ρ(film), or, if viewed fromthe gas side, the partition function,K=Δm(film)/V(film)/ρ(vap)=μ·ρ(film)/ρ(vap), both of which may be listedin the table of FIG. 8. The solubility of gases in polymers may bediscussed from a theoretical vantage point, and the experimental resultsof toluene and DMMP uptake in several polymers may be noted withpartition equilibria or coefficients, K=Δm/V(film)/ρ(vap), at roomtemperature, ranging from 1000 to 100,000 as shown in a graphical plotin FIG. 9, and with some numerical examples at room temperature given ina table in FIG. 10, for vapor-(non-porous) polymer pairs. In the table,PDMS=polydimethylsiloxane, PECH=polyepichlorohydrin, Latex˜polybutylene,ABACD=abietic acid, SEB=styrene/ethylene-butylene (powder),DMMP=dimethyl methylphosphonate, DEEP=diethyl ethylphosphonate, andDB-5=PDMS+5% phenyl substitution, a common GC film. As to DB-5, K=β·k′,with k′ may be from retention times (corrected for a temperature changefrom the experimental value of 100° C. to 25° C., see FIG. 11) for acolumn with 100 μm ID and 0.4 μm film thickness, β=61.7. FIG. 11 showsretention time and k′=(t_(r)−t_(o))/t_(o) (plotted as ln(k′)) versus 1/T(temperature in 1/K), for DEEP and DMMP.

As anticipated roughly by Raoult's law, the values for the more volatilecompounds (toluene relative to DMMP) may be much lower, and those forsmaller, more volatile molecules like hexane, may be lower still. TheGC-film DB-5 appears to adsorb less gas than the other polymers noted,despite chemical similarities between PDMS and DB-5 and apparentlywidely diverging values. A significant point is that the estimatedpartition equilibrium constants for various analytes on the presentporous sensor film with values of t₄, ρ_(La) and ρ_(ga) yield saturationk-values which may be worthy of note, as indicated in a table of FIG.12. That table reveals partition coefficients derived for porous NG-Efilms of an 800 m²/g specific surface area.

For the table of FIG. 12, the “quasi K-values at boiling point” may becomputed for an assumed monomolecular (liquid analyte) film inside allpores, which may then be converted to an equivalent analyte gaseousdensity fraction outside the pores but within the overall confines ofthe porous film. With the temperature dependence of k′, which may alsohold for K=k′·β, then the K-values may be converted from boiling pointto 22° C. The so-obtained equivalent K-values (22° C.) should then becomparable to K-values for non-porous films in the table of FIG. 10. Acomparison of these tables appear to show that the alkanes of increasingmolecular weight might increase as expected, and that the analyteK-values in the porous film may be generally higher than those innon-porous films.

Large partition coefficients may enable analytes to concentrate in thefilm at K-times greater concentration than the one in the gas phase,thus reaching monomolecular film coverage before reaching a 100%gas-phase concentration. Therefore, the low-vapor pressure analytes ofK˜100,000 may be detected at 1 ppm gas phase concentrations with acapacitance sensitivity, δC˜0.008 pF, rather than estimates of 0.08·10⁻⁶pF, corresponding to K˜1.

The present device may involve a monolithic micro GC pre-concentrator121, separator 123 (FIGS. 15 and 16), TCD (thermal conductivitydetector) 115, 118, flow sensor 122, p and T sensors, and a “thin-film”gas detector, e.g., CID 10. The present device may incorporate amonolithic micro GC system with a “thin-film” gas detector, in whichthis thin film may be the same active material in the three micro GCoperations—pre-concentration, separation and CID, after a spin-coatapplication on one wafer, which forms one of the channel walls of, forexample, concentrator 121 and/or separator 123. The micro GC may be aPHASED MGA 110. The noted “thin-film” material may consist of a porousfilm such as NGE (nanoglass-E), NGE+TA (toughening agent) or GX-3P asthe with TA materials, available from Honeywell International Inc.,rather than non-porous material films.

An advantage of the CID 10 may include greater sensitivity and speedcombination than conventional CIDs, as provided by the large-surfacearea of the open-pore film, which enables analyte to more rapidly adsorbor dissolve into and desorb from the film 15 in this CID 10, than with afilm of equal mass without pores. Another advantage may include thecapability of one and the same GC stationary film to serve forpre-concentration and separation (of devices 121 and 123, respectively),as well as for gas detection, i.e., to observe the elution time and thepeak area, to identify and quantify each analyte, respectively. Further,an application of the porous film via spin-coat on just one wafer toform one of the channel walls, may keep fabrication costs lower thanfabrication involving coating of all channel walls.

Separation performance of GC columns with partial stationary phasecoverage may be noted. Because k′ depends on i.e., the ratio ofgas/stationary phase volumes, stationary film temperature, and thestationary film thickness, then analyte molecules near the uncoated,wall may tend to elute without any retention (k′=0), whereas analytemolecules near the coated part of the column may be retained andcorrespond to k′>0, each of which is expected to result in significantdeterioration of achievable separation efficiency. Countering thiseffect may be a rapid and short time diffusion between the walls of the(square) column. It may be calculated that an increase in plate heightand associated loss in resolution in rectangular channels with only oneor two coated walls coated, relative to columns with the four wallscoated, shows that (the table of FIG. 13) for the square channels withone coated wall, the increased plate height is a factor of 1.50 relativeto one with all walls coated, and a factor of 1.92 relative to acylindrical column. These calculations appear to omit temperatureeffects. The table appears to concern separation impedances forpressure-driven systems. The retention factor k′ may equal =4. Codes infirst column may be as follows: “OT”=open cylindrical; “BT”=coating atbottom and top; “AL”=coating at all walls; “BO”=coating at bottom wallonly; numbers by the codes refer to width-to-height ratio, φ; “NE”=edgeeffects neglected; u_(m)=mean gas velocity; ν_(m)=reduced gas velocity;h=H/d_(c)=reduced plate height; H=plate height, d_(c)=column ID; andΦ=permeability factor.

Temperature effects may be noted. Because the PHASED MGA columns mayoperate with temperature control of just one wall, temperature ramping,as needed to achieve high-speed analyses, can cause temperaturegradients between the heated “wall” and the other uncoated ones.Fortunately, one may take advantage of the temperature-dependence of k′by applying a much thinner “coating” to the unheated walls, e.g., in theform of a thin “deactivation” film, which should exhibit smallerk′-values. During ramping, the lower temperatures of the cooler wallsmay qualitatively increase k′-values to approach the hot-wall values. Ifone selects the coating thicknesses carefully and remembering (FIG. 14)that for every 17° C. temperature drop, k′ may approximately double ortriple its value. FIG. 14, like FIG. 11, shows the retention time andk′=(t_(r)−t_(o))/t_(o) (plotted as ln(k′)) versus 1/T, for a number ofanalytes.

Performance of a GC separation column may be expressed by a performanceindex, π:

π=N ²/(t _(o) Δp),

where N=number of theoretical plates, t_(o)=elution time for unretainedpeak, and Δp=pressure drop; and in terms of its reduced plate height,h=H/d, which may have a theoretical minimum of h=1, and d=capillary ID.

Other polymers, such as Nafion™, a proton-conducting, perfluoro-polymer,may be considered as material for a polymer film for the CID 10.

The invention may incorporate a channel or channels for a flow of asample along a membrane that supports heaters and a stationary phase forsample analysis. The channel or channels may be an integral part of amicro fluid analyzer. The analyzer may have a pre-concentrator (PC)(viz., concentrator) and chromatographic separator (CS) thatincorporates the channel or channels.

FIG. 15 shows a pre concentrator 121 and a separator 123 for a fluidanalyzer 110. A CID 10 may be situated at an inlet of a pre concentrator121 and an outlet of a separator 123. The CIDs 10 may be connected in adifferential mode. A sample 111 may be moved with a thermal pump 46 inpre concentrator 121. The pump could instead be in the separator 123.The thermal pump 46 may have three heaters receiving sequencedenergizing signals to provide heat pulses by the heaters in a fashion tomove the sample fluid 111 through the pre concentrator 121 and separator123. Other kinds of thermal pumps may be used, or an ordinary pump 116(like that in FIG. 16) may be used. A controller 119 may provide signalsto the pump 46, and to heaters in the pre concentrator 121 and separator123 via contact pads 41. Controller 119 may process signals from theCIDs 10, and other detectors and flow sensor(s) (FIG. 16). Controller119 may have, for instance, a pre amplifier, an analog-to-digitalconverter (and vice versa), a timer, and a microprocessor. Themicroprocessor may manage and process signals from the CIDs 10, flowsensor(s), TCDs, and so on, and provide signals for power to theheaters, including the pump, and to detectors (e.g., TCDs) and sensorsas needed.

FIG. 16 is a system view of a fluid analyzer which may be a phasedheater array structure for enhanced detection (PHASED) micro gasanalyzer (MGA) 110. It reveals certain details of the micro gasapparatus 110 which may encompass the specially designed channeldescribed herein. The PHASED MGA 110, and variants of it, may be usedfor various chromatography applications.

Sample stream 111 may enter input port 112 to the first leg of adifferential thermal-conductivity detector (TCD) (or other device) 115.A pump 116 may effect a flow of fluid 111 through the apparatus 110 viatube 117. There may be additional or fewer pumps, and various tube orplumbing arrangements or configurations for system 110 in FIG. 16. Fluid111 may be moved through a TDC 115, concentrator 121, flow sensor 122,separator 123 and TDC 118. Controller 119 may manage the fluid flow, andthe activities of concentrator 121 and separator 123. Controller 119 maybe connected to TDC 115, concentrator 121, flow sensor 122, separator123, TDC 118, and pump 116. Data from detectors 115 and 118, and sensor122 may be sent to controller 119, which in turn may process the data.The term “fluid” may refer to a gas or a liquid, or both.

FIG. 17 is a schematic diagram of part of the sensor apparatus 110representing a heater portion of concentrator 121 and/or separator 123in FIG. 16. This part of sensor apparatus 110 may include a substrate orholder 124 and controller 119. Controller 119 may or may not beincorporated into substrate 124. Substrate 124 may have a number of thinfilm heater elements 125, 126, 127, and 128 positioned thereon. Whileonly four heater elements are shown, any number of heater elements maybe provided, for instance, between two and one thousand, but typicallyin the 20-100 range. Heater elements 125, 126, 127, and 128 may befabricated of any suitable electrical conductor, stable metal, alloyfilm, or other material. Heater elements 125, 126, 127, and 128 may beprovided on a thin, low-thermal mass, low-in-plane thermal conduction,membrane, substrate or support member 124, as shown in FIGS. 17 and 18.

In FIG. 18, substrate 130 may have a well-defined single-channel phasedheater mechanism and channel structure 131 having a channel 132 forreceiving the sample fluid stream 111. The channel may be fabricated byselectively etching a silicon channel wafer substrate 130 near thesupport member 124. The channel may include an entry port 133 and anexhaust port 134.

The sensor apparatus 110 may also include a number of interactiveelements inside channel 132 so that they are exposed to the streamingsample fluid 111. Each of the interactive elements may be positionedadjacent, i.e., for closest possible thermal contact, to a correspondingheater element. For example, in FIG. 18, interactive elements 35, 36,37, and 38 may be provided on a surface of support member 124 in channel132, and be adjacent to heater elements 125, 126, 127, and 128,respectively. There may be detectors 115 and 118 at the ends of channel132.

There may be other channels having interactive film elements which arenot shown in the present illustrative example. The interactive elementsmay films be formed from any number of substances commonly used inliquid or gas chromatography. Furthermore, the interactive substancesmay be modified by suitable dopants to achieve varying degrees ofpolarity and/or hydrophobicity, to achieve optimal adsorption and/orseparation of targeted analytes.

The micro gas analyzer 110 may have interactive elements 35, 36, . . . ,37 and 38 fabricated with various approaches, such that there is apre-arranged pattern of concentrator and separator elements are coatedwith different adsorber materials A, B, C, . . . (known in gaschromatography (GC) as stationary phases). Not only may the ratio ofconcentrator 121/separator 123 elements be chosen, but also whichelements are coated with A, B, C, . . . , and so forth, may bedetermined (and with selected desorption temperatures) to contribute tothe concentration and separation process. A choice of elementtemperature ramping rates may be chosen for the A's which are differentfor the B, C, . . . , elements. Versatility may be added to this systemin a way that after separating the gases from the group of “A” elements,another set of gases may be separated from the group of “B” elements,and so forth.

Controller 119 may be electrically connected to each of the heaterelements 125, 126, 127, 128, and detectors 115 and 118 as shown in FIG.17. Controller 119 may energize heater elements 125, 126, 127 and 128 ina time phased sequence (see bottom of FIG. 19) such that each of thecorresponding interactive elements 35, 36, 37, and 38 become heated anddesorb selected constituents into a streaming sample fluid 111 at aboutthe time when an upstream concentration pulse, produced by one or moreupstream interactive elements, reaches the interactive element. Anynumber of interactive elements may be used to achieve the desiredconcentration of constituent gases in the concentration pulse. Theresulting concentration pulse may be sensed by detector 118 for analysisby controller 119.

FIG. 19 is a graph showing illustrative relative heater temperatures,along with corresponding concentration pulses produced at each heaterelement. As indicated herein, controller 119 may energize heaterelements 125, 126, 127 and 128 in a time phased sequence with voltagesignals 50. Time phased heater relative temperatures for heater elements125, 126, 127, and 128 may be shown by temperature profiles or lines 51,52, 53, and 54, respectively.

In the example shown, controller 119 (FIG. 17) may first energize heaterelement 125 to increase its temperature as shown at line 51 of FIG. 19.Since the first heater element 125 is thermally coupled to firstinteractive element 35 (FIG. 18), the first interactive element desorbsselected constituents into the streaming sample fluid 111 to produce afirst concentration pulse 61 (FIG. 19), while no other heater elementsare not yet pulsed. The streaming sample fluid 111 carries the firstconcentration pulse 61 downstream toward second heater element 126, asshown by arrow 62.

Controller 119 may next energize second heater element 126 to increaseits temperature as shown at line 52, starting at or before the energypulse on element 125 has been stopped. Since second heater element 126is thermally coupled to second interactive element 36, the secondinteractive element also desorbs selected constituents into streamingsample fluid 111 to produce a second concentration pulse. Controller 119may energize second heater element 126 in such a manner that the secondconcentration pulse substantially overlaps first concentration pulse 61to produce a higher concentration pulse 63, as shown in FIG. 19. Thestreaming sample fluid 111 may carry the larger concentration pulse 63downstream toward third heater element 127, as shown by arrow 64.

Controller 119 may then energize third heater element 127 to increaseits temperature as shown at line 53 in FIG. 19. Since third heaterelement 127 is thermally coupled to the third interactive element 37,the third interactive element 37 may desorb selected constituents intothe streaming sample fluid to produce a third concentration pulse.Controller 119 may energize the third heater element 127 such that thethird concentration pulse substantially overlaps the largerconcentration pulse 63, provided by the first and second heater elements125 and 126, to produce an even larger concentration pulse 65. Thestreaming sample fluid 111 may carry this larger concentration pulse 65downstream toward an “Nth” heater element 128, as shown by arrow 66.

Controller 119 may then energize “N-th” heater element 128 to increaseits temperature as shown at line 54. Since “N-th” heater element 128 isthermally coupled to an “N-th” interactive element 38, “N-th”interactive element 38 may desorb selected constituents into streamingsample fluid 111 to produce an “N-th” concentration pulse. Controller119 may energize “N-th” heater element 128 in such a manner that the“N-th” concentration pulse substantially overlaps the largeconcentration pulse 65 as provided by the previous N−1 interactiveelements, to produce a larger concentration pulse 67. The streamingsample fluid 111 may carry the resultant “N-th” concentration pulse 67to either a separator 123 and/or a detector 118.

In the present specification, some of the matter may be of ahypothetical or prophetic nature although stated in another manner ortense.

Although the invention has been described with respect to at least oneillustrative example, many variations and modifications will becomeapparent to those skilled in the art upon reading the presentspecification. It is therefore the intention that the appended claims beinterpreted as broadly as possible in view of the prior art to includeall such variations and modifications.

1. An impedance detector comprising: a substrate; a dielectric layersituated on the substrate; a first electrode situated on the dielectriclayer; a second electrode situated on the dielectric layer; and apolymer layer situated on a portion of the first electrode, a portion ofthe second electrode, and an area of the dielectric layer between thefirst electrode and the second electrode; and wherein: the first andsecond electrodes are interdigitated electrodes; and the polymer layerhas a low dielectric constant due to a material property, and randompores and/or a MEMS-fabricated array of openings.
 2. The detector ofclaim 1, wherein: the first electrode comprises a first plurality offinger-like electrodes; the second electrode comprises a secondplurality of finger-like electrodes; and wherein the first plurality offinger-like electrodes is intermeshed, but not in contact, with thesecond plurality of finger-like electrodes.
 3. The detector of claim 2,wherein the electrodes comprise a porous structure.
 4. The detector ofclaim 3, wherein the electrodes are low-height and low-width electrodes.5. The detector of claim 1, wherein: the substrate is silicon; thedielectric layer is SiO₂; the electrodes comprise conductive material;and the polymer layer is a material having a low dielectric constant,porosity, and/or a high partition coefficient for a target analyte. 6.An impedance detector system, comprising: a first interdigitatedchemical impedance detector comprising: a substrate; a dielectric layersituated on the substrate; a first electrode situated on the dielectriclayer; a second electrode situated on the dielectric layer; and apolymer layer situated on the first electrode, the second electrode, andan area on the dielectric layer between the first and second electrodes;and a second interdigitated chemical impedance detector comprising: asubstrate; a dielectric layer situated on the substrate; a firstelectrode situated on the dielectric layer; a second electrode situatedon the dielectric layer; and a polymer layer situated on the firstelectrode, the second electrode, and an area on the dielectric layerbetween the first and second electrodes.
 7. The system of claim 6,wherein the first and second chemical impedance detectors are connectedin a differential mode.
 8. The system of claim 7, wherein: the firstchemical impedance detector is exposable to an analyte; and the secondimpedance detector is exposable to a reference sample, which may containa different concentration of the analyte.
 9. The system of claim 7,wherein the differential mode is an AC-coupled mode.
 10. The system ofclaim 6, wherein: the first electrode of the first chemical impedancedetector comprises a first plurality of finger-like electrodes; thesecond electrode of the first chemical impedance detector comprises asecond plurality of finger-like electrodes; the first electrode of thesecond impedance detector comprises a third plurality of finger-likeelectrodes; the second electrode of the second chemical impedancedetector comprises a fourth plurality of finger-like electrodes; thefirst plurality of finger-like electrodes is intermeshed, but not incontact, with the second plurality of finger-like electrodes; and thethird plurality of finger-like electrodes is intermeshed, but not incontact, with the fourth plurality of finger-like electrodes.
 11. Thedetector of claim 10, wherein: the polymer layer has a low dielectricconstant; the polymer layer is a porous thin film layer; the electrodesare low-height and low-width electrodes; and the electrodes are porous.12. The system of claim 6, further comprising: an array of chemicalimpedance detectors; and wherein: the first and second chemicalimpedance detectors are in the array of chemical impedance detectors;and each chemical impedance detector comprises: a substrate; adielectric layer situated on the substrate; a first electrode situatedon the dielectric layer; a second electrode situated on the dielectriclayer; and a polymer situated on the first electrode, the secondelectrode, and an area on the dielectric layer between the first andsecond electrodes.
 13. The system of claim 12, wherein: the firstelectrode situated on the dielectric layer comprises a first pluralityof narrow and lengthy electrodes; the second electrode of the chemicalimpedance detector comprises a second plurality of narrow and lengthyelectrodes; and the first plurality of narrow and lengthy electrodes isintermeshed, but not in contact, with the second plurality of narrow andlengthy electrodes.